| Proposed Dadu river Barak hydropower station locates in Jiaomuzu river section in Maerkang county of Aba Tibetan and Qiang Autonomous Prefecture in Sichuan Province, which is the 2th level hydropower station of hydropower planning "3 reservoirs & 22 levels " in main Dadu river, upper connecting with Xiaerxia steps, and down with Dawei power stations. The Guoerwu ramp in the right bank of the power station is about 600m long, 450m high, whose upper part is the Guoerwu erosion platform, covered with close-grained windborne sediment, and the type of the lower layer is complex, with small thickness. Bedrock is composed with granite and sand-slate. According to on-site survey, the unloading depth of granite and sandstone is generally high, with some sections of strongly weathered granite 50m long. Strong unloading leads the structures of the slope rock mass to be loosen. Once a sliding slope event occur,the normal operation of the proposed power station will be greatly influenced.This paper mainly studies the slope close to the reservoir bank of the dam of Barak power station. Firstly, the whole reservoir bank of the dam of Barak power station has been sectioned, and the Guoerwu ramp is considered as the key research object. Then, the engineering geological conditions, the structure characteristics and deformation characteristics of the slope rock mass of Guoerwu ramp have been comprehensively studied. Based on all the physical parameters of Gneis got by field tests and indoor tests, the stress state before water storage and the mechanism of deformation after water storage of Guoerwu ramp have been analyzed by FLAC3D , and the position of the potential sliding slope has been determined. Finally, the stability of slope is qualitatively analyzed through the analysis of field investigation materials, and the slope stability is calculated quantitatively by GEO-SLOPE software. The main achievements in this paper are as follows:(1)The reservoir bank close to the dam of Barak power station can be divided into five sections, by preliminary on-site exploration, Guoerwu ramp in the section of reservoir bank of Yala ditch ~ Daqiang ditch base terrace is covered by a deposit with large scope of yet undetermined thickness, and the unloading depth of granite is large. Thus, Guoerwu slope is determined as the main research object in the section of reservoir bank close to the dam of barak power station. (2)Through on-site investigation, the covered layer of Guoerwu slope is composed with Aeolian deposits, glacial debris, colluviums, slope wash and glacial mud-rock flows. The distribution elevation of layers are different, but with small thickness, and small amount. Even if the instability events occur, the normal operation of the reservoir will not be seriously influenced. The bedrock of Guoerwu ramp is weakly weathered, but with high unloading degree, loosen rock mass structure, and low mechanical strength parameters.(3)The rock mass can be divided into following four structures by the development of unloading fractures: entire-massive structure, lay-like structure, structure controlled by slow fissures and medium structure. Among which, strongly unloading - entirely & massive structure (A1), strongly unloading– rock controlled by steep fissures (B1) and strongly unloading–rock controlled by steep & slow fissures (C21) may occur instability and destruction. Through the on-site investigation, it can be found that the rock mass of Guoerwu ramp exist deformation and failure modes such as dump deformation, wedge sliding, plane sliding, and circular sliding .etc. But, these deformation and failure modes control limited areas, with no above 50m3 amount. Even if a sliding occurs, the safe operation of the reservoir will be not influenced seriously. Add up, the deformation of Guoerwu ramp mainly focused on the superficial department, and the deep rock mass shows no apparent deformation, which is consistent with no deep pull crack in on-site investigation.(4)The investigation on Guoerwu slope by FLAC3D shows that the slope is wholly stable in natural, with partially certain plastic deformation units, which are mainly shear deformation, but with limited range, and has not formed perforatively failure surfaces. In 2-2 profile, the steep-slow turning part in the back edge of the slope appears stress concentration phenomenon in a degree.(5)Through on-site investigation, there is no large-scale deformation in Guoerwu slope, which is in stable by the qualitative judgment. The results of the slope stability calculated by the equilibrium method for rigid blocks show that the slope is in stable before reservoir, even in the situation of occurring intense rainfall andⅦearthquake,but the emergency capacity of the 2-2 profile is low. After reservoir, each profile is in stable in various conditions. The potential slippery slope body of the 2-2 profile lies at the edge of the slope, so the reservoirfilling has no influence on the 2-2 profile stability. |
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